|
1 Department of Geology & Geophysics, University of Edinburgh, West Mains Road, Edinburgh EH9 3JW, UK
2 British Geological Survey, Murchison House, West Mains Road, Edinburgh EH9 3LA, UK SDAV{at}bgs.ac.uk
A new deep-water borehole at the foot of the West Shetland Slope revealed a sequence of Late Pleistocene glacimarine sediments. This section comprises an interbedded sequence of muddy diamictons, with subordinate sandy muds with dropstones and matrix-poor sands and gravels. Integration of core data, seabed imagery and high-resolution seismic-reflection records indicate the succession is dominated by stacked glacigenic debris flows.
Individual debris flows are composed of massive, clast-poor muddy diamicton, and are seperated by sandy muds and the sands and gravels. The mud units are interpreted as a combination of hemipelagic-glacimarine and distal ice-rafted deposits. The sands and gravels are interpreted as the result of bottom-current reworking of glacial and pre-glacial sediments. The new data support previous studies which suggest that Pleistocene ice sheets reached the edge of the West Shetland Shelf on several occasions, delivering large volumes of glacigenic sediment directly to the shelf edge and upper slope. These deposits became unstable, forming debris flows which transported the glacigenic sediments to the deep-water environment. Seabed imagery shows that the area around the borehole formed a focus for this style of deposition.
A depositional model constructed from the new data is enhanced by the application of data from an ancient deep-water, glacially-influenced, succession from the Neoproterozoic Macduff Formation NE Scotland.
